Problem: Solve for $x$ and $y$ using substitution. ${-x+2y = -9}$ ${x = y+5}$
Solution: Since $x$ has already been solved for, substitute $y+5$ for $x$ in the first equation. ${-}{(y+5)}{+ 2y = -9}$ Simplify and solve for $y$ $-y-5 + 2y = -9$ $y-5 = -9$ $y-5{+5} = -9{+5}$ ${y = -4}$ Now that you know ${y = -4}$ , plug it back into $\thinspace {x = y+5}\thinspace$ to find $x$ ${x = }{(-4)}{ + 5}$ ${x = 1}$ You can also plug ${y = -4}$ into $\thinspace {-x+2y = -9}\thinspace$ and get the same answer for $x$ : ${-x + 2}{(-4)}{= -9}$ ${x = 1}$